This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Vaginal ring devices are being developed to provide sustained release of HIV microbicides. To date, only limited pharmacokinetic data is available from animal or human studies. Here we report the effect of Depo-Provera pre-treatment, commonly used to thin the vaginal epithelium in challenge experiments, on the pharmacokinetic profile of CMPD167 (a small molecule CCR5 co-receptor antagonist) in rhesus macaques following vaginal ring administration. A single 400mg CMPD167 silicone elastomer vaginal ring was inserted into each of twelve female rhesus macaques. Six macaques were treated with Depo-Provera (DP) 30 days before ring placement;the other six macaques were untreated. Blood, vaginal fluid and vaginal biopsies were collected prior to and at various times during 28 days of ring placement and assayed for CMPD167 levels by HPLC. Significant differences (p=0.0003) were observed in mean daily vaginal fluid levels between the DP-treated (16-56 mcg/mL) and untreated groups (48-181 mcg/mL). Plasma CMPD167 levels were significantly higher peaking at 4 ng/mL and maintaining levels of 1-2 nM throughout the 14 days of testing in animals pre-treated with DP compared to non DP-treated macaques (1 ng/mL maintained).